152 THE AMERICAN MONTHLY [May 



luted on to a cell of paraffined millboard. In this condi- 

 tion I have preserved Lophopus and other Polyzoa for 

 forty-eight hours, including two nights' exhibition. The 

 following details may be found useful. 



The cell is composed of a piece of millboard about 2" 

 X 1^" ; in this a circular hole, f" — |" in diameter, is 

 punched by a wad-punch, as sold by the gunsmiths. The 

 cell is then immersed in a bath of melted paraflBn candle, 

 so long as bubbles rise ; it is then placed on a glass slide, 

 about 4" X 2", and left to cool : the side of the cell which 

 bears the burr from the punch must, of course, be upper- 

 most, or else it will not lie flat and stick to the slide ; a 

 number of these may be prepared at the same time, as 

 they keep for years, and travel very well. When the 

 time comes the cover-glass is laid on a flat surface, and 

 the weed bearing the objects is placed on it ; a needle may 

 be used to arrange it, if necessary ; or the drop of water 

 containing swimming organisms is gently put on it with 

 a pipette. The margin of the cover must then be wiped 

 with a corner of the handkerchief or a piece of thick blot- 

 ting-paper, by a succession of circular movements, each 

 over a short segment of the circumference; it is then left 

 for a little till the moisture dries off" from the wiped edge, 

 and it appears quite clean and shiny ; then, if necessary, 

 a little more water may be added in the centre with a 

 dropping-tube, a fine pipette, or even a pair of fine for- 

 ceps. The cover is next pushed to overhang the edge of 

 the flat surface on which it has been lying, taken up with 

 the fine forceps (which must be quite dry), and dexterous- 

 ly turned over and lowered on to the prepared cell so that 

 the drop is well over the centre of the hole. The edge of 

 the cover must then be luted on ; the instrument I use is 

 a coarse hairpin twisted into a ring near one end, pro- 

 duced beyond the turn for half an inch, and bent at a 

 right angle, the ring serving as a reservoir of heat. With 

 this it is easv to melt shreds of paraffin so as to seal the 



